The subject matter disclosed herein relates to premixed direct injection nozzles and more particularly to a direct injection nozzle having good mixing, flame holding and flash back resistance.
The primary air polluting emissions usually produced by gas turbines burning conventional hydrocarbon fuels are oxides of nitrogen, carbon monoxide, and unburned hydrocarbons. It is well known in the art that oxidation of molecular nitrogen in air breathing engines is highly dependent upon the maximum hot gas temperature in the combustion system reaction zone. One method of controlling the temperature of the reaction zone of a heat engine combustor below the level at which thermal NOx is formed is to premix fuel and air to a lean mixture prior to combustion.
There are several problems associated with dry low emissions combustors operating with lean premixing of fuel and air. That is, flammable mixtures of fuel and air exist within the premixing section of the combustor, which is external to the reaction zone of the combustor. Typically, there is some bulk burner tube velocity, above which a flame in the premixer will be pushed out to a primary burning zone. However, certain fuels such as hydrogen or syngas have a high flame speed, particularly when burned in a pre-mixed mode. Due to the high turbulent flame velocity and wide flammability range, premixed hydrogen fuel combustion nozzle design is challenged by flame holding and flashback at reasonable nozzle pressure loss. Diffusion hydrogen fuel combustion using direct fuel injection methods inherently generates high NOx.
With natural gas as the fuel, premixers with adequate flame holding margin may usually be designed with reasonably low air-side pressure drop. However, with more reactive fuels, such as high hydrogen fuel, designing for flame holding margin and target pressure drop becomes a challenge. Since the design point of state-of-the-art nozzles may approach 3000 degrees Fahrenheit bulk flame temperature, flashback into the nozzle could cause extensive damage to the nozzle in a very short period of time.